Opioids bind to opioid receptors and trigger the release of dopamine, a neurotransmitter that is associated with reward and pleasure. This creates a feeling of euphoria, which leads to an urge for more opioids.
This cycle of drug use gains momentum over time. People who start with small doses, quickly find that a low dose no longer gives them the high they first experienced. To experience that effect again, they take a higher dose until that no longer works.
Over time, people take higher and higher doses. This ultimately builds up to a high-dose daily opioid addiction that can be almost impossible to break away from without medical intervention and treatment.
What Makes Opioids So Addictive?
For most people, it is possible to take a prescription opioid like OxyContin or codeine for a brief period without developing an addiction. For others, however, even short-term use can lead to a psychological dependence long before physical tolerance begins.
Why do some people develop an addiction to opioids and others don’t? Several factors can contribute to the development of an addiction disorder, such as genetics, environment, and stress. While not everyone will experience all these factors, most people who develop an opioid use disorder (OUD) will struggle with one or more.
These are some of the reasons that opioids are so addictive:
Effect on Brain Chemistry
Opioids are a class of drugs that have a strong effect on brain chemistry, more so than most other substances of abuse.
The release of dopamine that happens with the use of opioids is compounded by a blocked reuptake of the neurotransmitter. This means that a larger amount of the feel-good chemical is released into the brain than normal, and it’s not reabsorbed as quickly as it would naturally, creating a high in the user.
This high can be immediately psychologically addictive. With continued opioid use, the person will need more of the drug in order to get high to the same extent. They may feel as if they are unable to experience peace or joy without use of the drug. If they struggle with chronic physical pain as well, it can contribute to perceived need for the drug.
Tolerance for Opioids
Physical tolerance can develop with a number of different medications, not just opioids, and it does not always lead to addiction. However, in the case of opioids, tolerance means that a person must take increasingly higher doses in order to experience the same pain-relieving effects. Since pain relief comes with a potential high in these cases, it can quickly lead to psychological dependence as well.
Tolerance plus psychological dependence lead to addiction. With increased use of the drug, the risk of experiencing associated risks, such as opioid overdose, organ damage, and other issues increases as well.
Physical Dependence & Opioid Withdrawal
Physical dependence occurs when the body adjusts its function based on the presence of opioids in the system. Over time, chronic opioid use alters the size and shape of brain cells, changing how they function, creating a need for opioids in order to achieve balance within the system.
Because the body and brain perceives that opioids are necessary for basic functioning, if levels of opioids in the system drop, withdrawal symptoms appear quickly. They may include anxiety, restlessness, muscle aches, nausea, and intense cravings for the drug.
Because opioid withdrawal symptoms can last for weeks and be so intense, many people relapse when they try to stop using opioids. For this reason, it’s recommended to undergo opioid detox with the support and supervision of addiction treatment professionals. Relapse during a period of abstinence can be fatal.
Psychological dependence occurs when an emotional dependency on opioids develops, causing the person to feel compelled to use the drugs. This may develop before or after the physical dependence, but it is more common among those who are struggling with chronic pain or a mental health disorder like anxiety or depression that is soothed with the use of opioids.
When this happens, the person may feel that they are unable to handle their mental health symptoms or their chronic pain without the use of opioids. As a result, they compulsively use opioids.
When opioids are readily accessible, people may try them, even if they never would have sought them out on their own. This can happen in a home where unused medications are stored in community medicine cabinets. For this reason, safe disposal of all excess opioid painkillers prescribed for the management of acute pain after an injury or surgery is recommended.
The potency of a given opioid can also increase the likelihood of addiction development. The stronger the drug is, the more intense the high experienced, and the more likely it is that someone will continue to seek out the drug.
- Basic opioid pharmacology: an update. Pathan H, Williams J. British Journal of Pain. 2012;6(1):11-16.
- Opioid tolerance development: A pharmacokinetic/pharmacodynamic perspective. Dumas EO, Pollack GM. The AAPS Journal. 2008;10(4).
- Opioid addiction, genetic susceptibility, and medical treatments: A review. Wang SC, Chen YC, Lee CH, Cheng CM. International Journal of Molecular Sciences. 2019;20(17).
- The brain on opioids. Ballantyne JC. PAIN. 2018;159:S24-S30.
- Prescription opioids | CDC’s response to the opioid overdose epidemic. Centers for Disease Control and Prevention. Published June 17, 2021. Accessed December 21, 2023.
- The neurobiology of opioid dependence: Implications for treatment. Kosten T, George T. Science & Practice Perspectives. 2002;1(1):13-20.
- Opioid withdrawal. Mansi Shah, Huecker MR. StatPearls. Published June 4, 2019. Accessed December 21, 2023.
- Disposal of unused medicines: What you should know. U.S. Food and Drug Administration. Published 2019. Accessed December 21, 2023.